The present invention relates to an automatic strobe apparatus for use with a diaphram-shutter of the type having a programmed operation wherein a selected ratio is, in daylight synchronized flash photography, maintained between proportions of the ambient scene light and the artificial scene light each directly contributive to the film exposure.
In against-the-backlight photography wherein illumination falls on the main subject in a scene from behind, a dissatisfactory-or-under-exposure of the main subject is generally caused regardless of a satisfactory-or proper-exposure of the scene. When applying a daylight synchronized flash photography technique to the aforementioned case, a proper exposure of the backlit subject is caused as well as the proper exposure of the scene because the artificial illumination provided by an electronic flash or strobe falls on and is then reflected by the main subject, resulting in the contribution thereof to the film exposure. On the other hand, when the intensity of ambient scene illumination light existing in the scene to be photographed (which in generally referred to as scene brightness) is relatively low as in indoor photography or outdoor photography in the early morning or late evening the ambient scene illumination light changes in color temperature, resulting in that the ambient scene illumination light differs in color quality from that for which a film is balanced, that is in a worse color reproduction. Even under such conditions, however, it is possible to develop the color reproduction by applying a daylight synchronized flash photography technique because of the strobe light close being in color temperature to the sunlight.
Recently, there has been proposed in Japanese unexamined published Pat. No. 149022/81 a fill-in flash system wherein it is intended to provide artificial illumination light to fill in the photographic subject against a backlit scene every exposure. The patent shows an electronic flash apparatus or system in combination with a specialized flashmatic mechanism which essentially comprises a photo-interrupter operatively associated with a focus adjusting ring for focusing an objective lens and a sensor plate which, in turn, is disposed between interrupter blades for the motion in association with the motion of the blades of the shutter mechanism of the type operated in programmed mode. The electronic flash apparatus is arranged to be fired at the time the aperture of the size determined by the flashmatic mechanism is established, the amount of illumination light provide by the electronic flash being previously determined corresponding to the level of ambient scene illumination light intensity. Under conditions of ambient scene illumination light intensity lower than that where no ambient scene illumination light contributes to the film exposure, the electronic flash is controlled to maintain its maximum amount of illumination light. But, under conditions of ambient scene illumination light intensity between the aforementioned intensity of no contribution of ambient scene illumination light to the film exposure and the intensity which causes the maximum exposure interval allowable for the exposure without incurring any adverse blurring effect from camera shake, the amount of illumination light provided by the electronic flash is varied in inverse proportion to the level of the ambient scene illumination light intensity. Furthermore, under conditions of ambient scene light intensity higher than that for the aforementioned maximum exposure interval, the minimum amount of illumination light from the electronic flash may be maintained, establishing the ratio of 35 percent of artificial illumination light centribution to the film exposure. In this case, the contribution of ambient scene illumination light to the film exposure is maintained in the ratio of 75 percent.
One of the problems associated with cameras utilizing an electronic flash apparatus having the aforementioned specialized flashmatic mechanism for daylight synchronized flash photography is concerned with the particularity in the operation of the shutter mechanism characterized by that, when ambient scene light intensity is relatively high and the subject to be photographed is at a distance, the commencement of the shutter closing operation is caused in advance of attaining its predetermined aperture size in accordance with the distance. The aforementioned particularity in the operation of the shutter mechanism results in an extremely reduced proportion of artificial illumination light contributing to the film exposure because of the fact that the electronic flash is, as in conventional units, fired in synchronism with the commencement of the shutter closing operation in disregard of the insufficiently attained aperture size of the shutter, so that it is dificult to accurately control the electronic flash to provide proportional illumination light. The electronic flash apparatus described above, from a different stand point, has an intricacy due to the provision of both the specialized flashmatic mechanism using a photo-interrupter and means for determining durations of time during which the electronic flash continues to provide illumination light.